# File src/ruby_supportlib/phusion_passenger/platform_info/apache.rb, line 343
    def self.httpd_infer_envvar(varname, options = nil)
      if envfile = httpd_envvars_file(options)
        result = `. '#{envfile}' && echo $#{varname}`.strip
        if $? && $?.exitstatus == 0
          return result
        else
          return nil
        end
      else
        return nil
      end
    end